1. Field of the Invention
The presently disclosed subject matter relates to an image pickup device and an endoscope, and particularly to a technology to prevent dew condensation on a cover glass disposed on the image pickup plane side of an image pickup element.
2. Description of the Related Art
An endoscope includes an insertion part to be inserted into a body of a subject. At the distal end part of the insertion part, an observation optical system which is made up of lenses and prisms is provided. An image pickup device is disposed at an image formation position of the observation optical system. An observed image is taken by the image pickup device through a lens and is subjected to a photo-electric conversion. An electrical signal after photo-electric conversion is appropriately processed at a processor, and is thereafter outputted to a monitor/TV so that the observed image is displayed on the monitor/TV.
In general, an image pickup device includes a solid-state image pickup element and a cover glass spaced apart at a fixed distance (gap) from the solid-state image pickup element. This gap allows the elimination of the attenuation of light thereby improving the light condensing efficiency of a micro-lens layer of the solid-state image pickup element.
However, providing a gap may cause a problem of dew condensation. When a gap is formed in an image pickup device, water vapor may permeate into the gap to be absorbed into a micro-lens etc. (resin) of the solid-state image pickup element during cleaning and inspection of the endoscope. Then, upon operation of the solid-state image pickup element, it generates heat. Due to this heat generation, the moisture absorbed in the micro-lens etc. (resin) is released into the gap resulting in a dew condensation on the surface of the cover glass. Since the dew condensation is picked up as an observed image by the solid-state image pickup element, it may cause a degradation of the visibility thereof leading to a misdiagnosis.
Methods for preventing dew condensation within an image pickup device have been proposed. In Japanese Patent Application Laid-Open No. 2007-260190, an endoscope apparatus, in which a prism is optically connected with a solid-state image pickup element via a cover glass, is provided with a heater affixed to the rear surface of the prism. By actively providing heat to the cover glass through the heater, the temperature difference between the solid-state image pickup element and the cover glass is reduced thereby preventing dew condensation.
In Japanese Patent Application Laid-Open No. 2003-284686, an image pickup device for an endoscope in which a cover glass and a solid-state image pickup element are optically connected is provided with a peripheral circuit disposed adjacent to the cover glass. As the result of the cover glass receiving the heat generated from the peripheral circuit, the temperature difference between the outer and inner surfaces of the cover glass can be reduced even when the distal end of an insertion part is rapidly cooled. Thereby, dew condensation on the inner surface of the cover glass is prevented.
In Japanese Patent Application Laid-Open No. 2000-147391, an image pickup part of an endoscope is made up of a combination optical system, a solid-state image pickup element, and a partition wall for optically connecting the both. A gap is made up of the combination optical system, the solid-state image pickup element and the partition. A vent hole is provided in the partition wall so that the gap is in communication with the outer space. Thereby, the water vapor produced in the gap due to heat generation from the solid-state image pickup element is discharged to the outer space.